A man who registered as a Green Party candidate for Montana's U.S. Senate race was on the state Republican Party's payroll and heads a newly formed anti-tax group, according to a review of election documents.

Timothy Adams filed as a challenger Monday against Democratic Sen. Jon Tester, who faces a tough re-election campaign, in a race where a Green Party candidate could siphon votes from the Democrat.

The Green Party qualified as a political party in Montana on Monday, which was also the state's deadline for candidates to file for office. Green Party officials blasted an email that morning to solicit candidates who could register by the day's end.

Adams was one of six people to file as a Green Party candidate for the races on the ballot this fall. A total of seven people are looking to unseat Tester, including four Republicans vying for their party's nomination.

Adams' name and phone number is the same as the treasurer of Montanans Against Higher Taxes, a group formed to oppose a legislative referendum on the ballot this fall for a 10-year property tax extension for the state's university system.

Adams also is accusing the pro-ballot referendum committee of campaign finance violations in a complaint filed with the Commissioner of Higher Practices last month. In that complaint, he lists the same phone number and a home address in Bozeman.

In his Senate filing, he lists a Three Forks post office box as his address. The reason for the disparity was not immediately clear.

Adams did not return calls for comment on Monday and Tuesday.

That same Bozeman address was listed under Adams' name in Federal Election Commission documents, showing Adams was paid by the Montana Republican State Central Committee from October 2013 through May 2015. His role with the party was not clear.

Adams also filed to run as a Libertarian candidate in a state House race in 2012, but later withdrew.

Green Party state coordinator Danielle Breck said she spoke to all of the candidates who filed under the party's name, including Adams. She said she reviewed with the candidates the Green Party's four pillars and 10 key points, which include ending war, halting dependence on fossil fuels and advocating for social justice.

"We don't actually have any ability to deny candidates to file under our name," Breck said.

She noted that another person, Steve Kelly of Bozeman, also filed as a Green Party candidate for the Senate race. There will be a primary election to determine the party's nominee, if both candidates stay in the race.

"We will absolutely vet both of those candidates," she said.

As of Tuesday, no Green Party candidate filed for the Senate race with the Federal Election Commission, according to the FEC website.